Effects of Inbreeding in Mimulus Guttatus on Tolerance to Herbivory in Natural Environments

Abstract

Inbreeding, which is common in plants, may increase the vulnerability of populations to natural enemies. Similarly, natural enemies may increase the expression of inbreeding depression in their hosts, resulting in altered selection on host mating-system evolution. To examine effects of inbreeding on tolerance to herbivory, we transplanted experimentally self-and cross-fertilized plants into four field populations of Mimulus guttatus and applied single Philaenus spumarius (spittlebug) nymphs to half. At the end of the growing season, we scored plants for five fitness components (reproductive effort, biomass, survival, probability of producing flowers or buds, and probability of bolting). Inbreeding reduced population-level tolerance to spittlebug herbivory with respect to plant aboveground biomass. Inbreeding effects on tolerance varied significantly among plant families for three fitness traits, indicating the opportunity for selection by herbivores to improve tolerance in inbreeding populations. These results also indicate that herbivores can alter inbreeding depression in plants. Our results mirror earlier greenhouse studies of inbreeding effects on plant-herbivore interactions, and demonstrate that these effects can be manifested in natural settings as well. This study indicates that inbreeding in natural populations can affect fitness not only directly, but also indirectly through altered interactions with natural enemies.

Genetic variation and constraints on the evolution of defense against spittlebug (Philaenus spumarius) herbivory in Mimulus guttatus

“…This model, however, does not include costs of tolerance, whereas such costs have been reported in other studies of tolerance to herbivory (Stowe et al, 2000). We also found no evidence for dominance variation for tolerance, even though previous experiments, involving this population as well as others, reported considerable variation among families in the response of tolerance to experimental self-fertilization (Carr and Eubanks, 2002;Ivey et al, 2004). The lack of significant dominance variation for tolerance in our diallel cross suggests that these earlier observations were due to mutations unique to family lines (Schultz and Willis, 1995).…”

“…The mating system of M. guttatus varies from approximately 75% selfing (t ¼ 0.25) to complete outcrossing (t ¼ 1.0), with a species mean tE0.6 (Ritland and Ritland, 1989;Dudash and Ritland, 1991;Willis, 1993). Inbreeding depression is commonly observed in M. guttatus (Carr and Dudash, 1996;Carr and Eubanks, 2002;Ivey et al 2004). Voucher specimens of native plants from the population studied herein (M13: Napa County, California, USA, 38133 0 N, 122122 0 W) are housed in the Illinois Natural History Survey herbarium.…”

“…Infested plants typically hosted 1-2 spittlebug nymphs, and fewer than half of plants hosted spittlebugs (CT Ivey and DE Carr, personal observation). A single spittlebug nymph can exact significant costs to the survival and reproductive success of M. guttatus in the field (Ivey et al, 2004). Because spittlebug attack is costly to plant fitness and attack rates are variable among plants, the potential for some mechanism of defense to evolve seems likely.…”

Inbreeding depression in adaptive plasticity under predation risk in a freshwater snail

“…While this perspective has yielded great insights, mounting evidence demonstrates that inbreeding effects are environment-dependent (e.g. Bijlsma et al 1999;Carr & Eubanks 2002;Ivey et al 2004;Armbruster & Reed 2005;Waller et al 2008). There is a great diversity of mating systems in nature (Goodwillie et al 2005;Jarne & Auld 2006), and the role of environmental conditions in the evolution of mating systems is increasingly discussed (e.g.…”

Effects of Florivory and Inbreeding on Reproduction in Hermaphrodites of the Wild Strawberry Fragaria virginiana

“…It is well known that the expression of inbreeding depression can vary with environmental conditions (Hauser and Loeschcke 1996;Cheptou et al 2000;Steets et al 2006;Botham et al 2009), and the herbivore environment is no exception (Carr and Eubanks 2002;Ivey et al 2004;Koslow and Clay 2007;Leimu et al 2008); however, the direction of the effect can be quite variable. For instance, in Lychnis flos-cuculi inbreeding depression was reduced in the presence of snail herbivores because the snails depressed fruit production of outcrossed plants more than selfed plants (Leimu et al 2008).…”